Follow the guidelines provided in this article to resolve a Windows 10 Activation Error Code 0xC004C008 (Product key already in use) on system activation out of the box (OOB).
Error Code 0xC004C008
You may encounter a Windows 10 activation issue on a new system received from Dell. On the initial system boot, you may see the following error (Figure 1):
Figure 1: Windows 10 activation error that product key is already in use
This error is caused by the activation server being aware that the Windows 10 product key may have been used on multiple PCs. When you install the Windows 8.1 or Windows 10 Operating System product a specific number of times, the error code 0xC004C008 normally prompts because the Windows 8.1 or Windows 10 license can only be installed on a single device.
Solution
NOTE: Some activation errors can be resolve simply by performing a couple of system reboots and then retrying the activation sequence. Reference :Microsoft Windows IT Center Article: Windows 10 edition upgrade
You can also refer to the Activation Troubleshooter to try and solve this issue. The troubleshooter will expedite the download of a required update for OA3 (OEM Activation Process 3.0).
If the issue continues to occur, then Contact Microsoft by dialing the Support number listed on the activation screen ("in the United States and Canada for example: 1-800-936-5700") and explain that the error message you are receiving is on a new Dell computer.
Microsoft will be able to provide phone activation.
If you're unable to activate Windows 10, the Activation troubleshooter could help. To use the troubleshooter, select Start > Settings > Update & Security > Activation , and then select Troubleshoot .
Error code 0xC004C003 is caused when trying to active the Operating System which uses an OEM Activation 3.0 Digital Product Key. More information about the error, can be found: KB5001692: Windows Activation fails with error 0xc004c003. The issue can be resolved by updating Windows to a later version.
Some of the personalization features in Windows Settings are greyed out if you don't activate Windows. You cannot change the Windows desktop wallpapers, windows colors and themes, customize Start menu/taskbar/lock screen/title bar/fonts, etc. Still, you cannot use Windows Dark Mode.
A digital license (called a digital entitlement in Windows 10, Version 1511) is a method of activation in Windows 10 that doesn't require you to enter a product key.
Select the Start button, then select Settings > Update & Security > Activation > Change Product Key, then enter the product key. If you installed a retail copy of Windows 10 on your device using a Windows 10 product key and then made hardware changes, follow this same process using your Windows 10 product key.
Open Settings.Click on Update & Security.Click on Activation.Confirm Activation is set to "Windows is activated with a digital license" under the "Windows" section.
Your license has been incorrectly signed. The Microsoft software downloaded by you is corrupted or your installation is failed. Windows registry is corrupted or damaged. Windows system file is damaged.
After the installation is complete, Windows 10 will automatically be activated online. To check activation status in Windows 10, select the Start button, and then select Settings > Update & Security > Activation . If Windows 10 isn't activated on your device, see Get help with Windows activation errors for more info.
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NOTE: Some activation errors can be resolve simply by performing a couple of system reboots and then retrying the activation sequence. Reference :Microsoft Windows IT Center Article: Windows 10 edition upgrade 
